High-voltage electrical insulating bushing



Filed April 26, 1950 Irventor` Philip A. Ewe- His Attohey Patented Jan.26, 1954 HIGH-VOLTAGE' ELECTRICAL INSULATING BUSHING Philip A., Ewe'London, England, assignor to; General Electric: Company.. a. comorationof New York Application April'26, 1950, Serial No. 158,238

Claims. priority application Great Britain May 17, 1949 1 Claim.

Thisinvention relates to high' voltage electrical insulating bushingsand more 'particularly to bushings in which the electrical stresses aresufiiciently high to make desirable the rounding off or screening ofprojecting metal parte sc as to avoid the formation of corona.

In order to provide suitable electrical connection between tank-enclosedelectrical equipment and the external circuits to which such equipmentis connected, it is standard practice to use an insulating bushingassembiy which passes through the top or side of the tank or enclosurein which the electrical equipment is contaired. such a bushing assemblyincludes a center conducting member, an insulating structure concentricof the conductor, and a metal grounding sleeve which is substantiallycentraliy located along the axis of the bushing structure and is themeans by which the bushing assembly is maintained in position withrespect to the tank casing. The outer portions of the insulatingstructure generally include tapered shell-like members, usually of aceramic material, which extend from the centrally-located groundingsleeve to the opposite ends of the conducting member.

In the case of high voltage bushings, where the potential between thecenter conducting member and the grounded metal casing in which theelectrical apparatusis contained is of a high magnitude, andparticularly where the end of the bushing structure contained inside thetank is immersed in oil, it is common practice to provide the end of theconductor which projects axially beyond the insulating members of thebushing structure inside of the enclosing tank, with a smooth contour,such as that of a spheroid, so as to avoid the exposure of any sharpedges from which corona may spring. This smooth contour is frequentlyprovided by an auxiliary metal conducting member which is attached inany suitable manner to the end of the conductor where it projects beyondthe insulating portions of the bushing.

In prior constructions, the joint between the conducting member or theauxiliary metal housing providing the smooth contour and the insulatingshell member has been in a flat plane normal to the axis of theconducting member.

It is an object of this invention to provide a new and improved jointstructure between the insulating shell member and the conducting membersat the tank-contained end of an elec trical bushing.

It is a further object of my invention to provide' a joint structurebetween the conducting members and the insulating shell at thetankcontained end' of an electrical bushing which will facilitate theaccurate concentric assembly of the conducting members and insulatingshell.

It is a further objectof my invention to provide a joint between theconducting members and the insulating shell membercf an electricalbushing which will result in lower electrical Stress at the surfacewhere the insulating shell member engages the conducting members.

It is a further object of this invention to provide a new and improvedjoint between the insulating member and conducting members of anelectrical bushing which permits a reduction in the dimensions of themetal conducting parts in proximity to the joint.

In accordance with these objectives, this invention` provides afrusto-conical joint between the. insulating shell and the conductingmembers of an electrical bushing with the external surface of the endof' the smooth-contoured electrical conducting member constitutng anextension of the frusto-conical: surface of' the joint.

The features of this invention which I believe to be novel are set forthwith particularity in the appended claim. My invention itself, however,both as to its organization and use, together with further objects andadvantages thereof, may best be understood by reference to the followingdescription taken in connection with the accompanying drawing whichshows a partially cutaway sectional View of the portion of an electricalbushing assembly embodying the frusto-conical joint of my invention.

Referring now to the drawing, there is shown a center conducting memberl, which may be in the form of a metal tube, surrounded by an outerinsulating shell of any suitable material and configuration, such as aporcelain petticoated shell 2. The space between the conducting member iand the outer insulating shell 2 may be filled with any suitabledielectric medium or may, as shown in the drawing, be provided withconcentric insulating cylinders 3 of any suitable material, the lowerends of which abut against the interier surface of the outer insuiatingshell member 2. The use of such insulating cylinders is conventional inthe electrical insulating bushing art, and forms no part of thisinvention.

In order to provide a suitable support member for insulating shell 2,the lower end of conducting member I is provided with a concentricconducting member 4 which acts as a bearing or support for insulatingshell 2. In accordance with my invention, the surface of support member4 which is adjacent shell member 2 is of a trustoconical shape orcontour.

The insulating shell member 2 is constructed. with a taper as itapproaches the joint, the bottom surface of shell member 2 beingparallel to the surface of support member 4 to which it is adjacent. Thefrusto-conical surface at the joint is made approximately normal to theexternal and internal wall surfaces of the insulating shell 2. Theconcentric conducting member 4 may be screwed onto the lower end ofconducting member I, or may be secured to conducting member I in anyother suitable manner.

In order to minimize the electrical Stress between the conductor l andgrounded metal surfaces to which it may be adjacent, a member having asmooth outer contour is provided 'at the end of conductor member i.Thismember with the smooth external contour is preferably in the formofa hollow metal bell-shaped member 5, the rim 6 of which forms anabutment against which the end of insulating member '2 is seated. Theouter end of member 5 is rigidly attached to the outer end of conductorI by any suitable method. It may be connected clirectly to abutmentmember 4 or it may be connected to a separate collar or sleeve member 'las shown in the drawing.

The frusto-conical surface at the joint between members 2 and 4 is madeapproximately normal to the walls of the tapered insulating shell, asmentioned hereinbefore, and the rim 6 of the rounded metal member :5 issubstantially tangential to the frusto-conical surface of the joint atthe point of departure of member 5 from the external wall of theinsulating shell 2.

Due to my invention, the conical form given to the engaging surfaces atthe joint between 2 will assist in the accurate concentric assembly ofabutment member 4 and insulating shell 2. Also, with my Construction, itis possible to provide a smooth-contoured member 5 having AO theabutment member 4' and the insulating shell a smaller overall diameterfor a given radius While there has been shown and described a.particular embodiment of my invention, it will be obvious to thoseskilled in the art that various changes and modifications can be madetherein without departing from the invention and, therefore, it is aimedin the appended claim to cover all such changes and modifications asfall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

An electrical insulating bushing comprising a conducting member, ahollow insulating member concentrically surrounding said conductingmember in spaced relationship, a metal support member for saidinsulating member positioned concentrically about said conducting memberadjacent an end thereof, said support member being rigidly attached tosaid conducting member and forming a continuation of a conductingsurface of said conducting member, said support member having afrusto-conical exterior surface, the apex of said frusto-conical surfacepointing away from said end of said conducting member, a transverse endsurface of said insulating member being frusto-conical and parallel tothe frusto-conical surface of said support member, a hollow metal memberhaving a rounded surface substantially surrounding said end of saidconducting member and said support member for reducing electrical Stressin the vicinity thereof, said hollow member having a rim portioninterposed between said frusto-conical surfaces of said insulating andsupport members, opposite surfaces of said rim portion abutting saidfrustoconical surfaces of said insulating and support members, adjacentsurfaces of said insulating member, rim portion, and support memberforming a rusto-conical joint.

PHILIP A. EWER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,129,468 Fo'tescue Feb. 23, 1915 1,350,925 Faccioli Aug. 24,1920 1,522,215 Wagner Jan. 5, 1925 1,749,419 Rump May 20, 1930 1,957,982Smith May 8, 1934 2,396,871 Meyerhans Mar. 19, l946

